1. Field of the Invention
This invention relates to a process for decomposing persistent substances, including environmental contaminants, more particularly a processing system for dissolving chlorofluorocarbon gas, plastics, such as polystyrene, wood, organic compounds which have a benzene nucleus, and other persistent substances of industrial wastes, in a superheated steam atmosphere by using thermal cracking, hydrolysis, reduction, oxidation, and combinations thereof.
2. Background of the Invention
Chlorofluorocarbon gas used as a refrigerant, and halogen gas used as an extinguishing agent are indicated to be environmental contaminants, so that a process for converting these substances into harmless substances has now became a world-wide concern in regards to preserving the global environment. Thus, several means to solve these problems have already been proposed. For example, a process for decomposing chlorofluorocarbon (trichlorofluoromethane, etc.) has been proposed, which uses such processes as, hydrothermal reaction, burning, cracking by explosive reaction, biochemical decomposition, ultrasonic dissolving and plasma reaction.
Among these processes, the hydrothermal reaction is considered to be a general purpose processing system which is applicable to any substances to be decomposed, including mainly, waste such as organic solvents like Trichlene (trichloro ethylene), waste oil, dioxin, PCB, feces etc. It can decompose, for example, chlorofluorocarbon gas into safe substances, such as sodium chloride and carbon dioxide.
To implement a device which uses hydrothermal reaction, experiments using an autoclave have been conducted, for example, in laboratories under conditions of mixing ratios for caustic soda, ethanol, and chlorofluorocarbon; and time settings for temperatures; pressure reaction times setting, and the reaction is conducted under the condition that it is kept at a high temperature of 300-450 (xc2x0 C.) with the high pressure of 100-250 kg/cm2.
The application of the present invention has proposed the process and device for decomposing environmental contaminants by using the hydrothermal reaction process mentioned above in Japanese patent Application Heisei-6-2045 19. The content of the Application will be briefly reviewed here, referring to the flowchart of the chlorofluorocarbon decomposition process shown in FIG. 13, wherein the tank 1 for storing liquid mixtures of chlorofluorocarbon liquid, caustic soda, and ethanol, and the liquid is send by the pump 2 via the flow meter 3 and the piping 3 to the heat exchanger 5. It is in turn sent to the hydrothermal reactor 6 in which hydrothermal reaction occurs, before being returned to reactor 5 and further sent via the cooler 7, the pressure regulating valve 8 to the separator 9 which separates the liquid into the pure water and substances. The tank 1a, the pump 2a and the flow meter 3a shown in FIG. 13 comprise a system which is used if the chlorofluorocarbon belongs to the type which is gasified at a normal temperature.
Each of the pumps 2 and 2a use a normal slurry pump. It requires a high force feed pressure produced by a vacuum of suctioning, and a good volume efficiency, and uses a force feed cylinder for high density slurry, pulverulent body mixed slurry, and acid or alkali slurry.
The reactor 6 has such an arrangement that the liquid mixture flowing via the heat exchanger 5 is led into the inlet 11, and it then flows through the piping 12 around which the band heater 13 is wound to exit from the outlet 14 as shown in FIG. 14. The band heater 13 has a suitable number of heaters, which are disposed along the piping 12, keeping each other within a suitable distance, and being controlled to have a constant temperature inside of it. Further, the cooler 7 has normal cooling equipment formed around the reactor tube to provide a pass way for the cooling water.
Heat decomposing equipment is disclosed in the Japanese Patent Laid-Laid-open Publication No. 58-56396, wherein superheated steam, which is generated by a superheated steam generator, is ejected into a decomposing furnace to separate or decompose waste tires into residue, such as decomposed gas and carbon dust, and tire bead for reuse. Also, in the Japanese Patent Application TOKKAIHEI 3-12220 a hydrolysis process is disclosed, wherein sodium fluoride alkane (Freon) is put in contact with a catalyst, made of activated carbon, carrying ferrous oxide in the presence of steam to convert it into harmless compounds.
As indicated above, the hydrothermal reactor 6 is required to be operable at a high temperature with a high pressure, so that it correspondingly makes the pressure regulating valve 8 have a complicated structure, resulting in a high price, and there is difficulty in designing its structure to have sufficient mechanical strength against such pressures as tensile stress, and thermal stress. A mechanism which is required to operate at a high temperature with a high pressure, has problems because it becomes complicated in its structure; has to be changed in order to meet with the type of decomposing substances, and is difficult to control in operation. In response to the high pressure, the piping 4 often fractures during operation, so that difficulty remains from the point of view of safety.
The hydrothermal reaction process mentioned above comprises a closed system, but such methods as rotary kiln process or incineration process are required to provide some measures against dioxin that is produced during the processing. It is also difficult for other processes to change the reacting process in order to meet the substances that are to be decomposed, and has some defect that it requires high running and initial costs since it requires a dedicated equipment, therefor it has little generality.
The thermal decomposing equipment disclosed in aforementioned Japanese Patent Laid-open Publication No. 58-56396 can decompose waste tire into wastes such as cracked gas carbon and carbon. It does not refer to any effective decomposition of persistent substances, such as chlorofluorocarbon which are subjective substances of the present invention, and cannot be practised to decompose the persistent substances. Also, the process as disclosed in the Japanese Patent Laid-open Publication No. 3-12220, in which chlorofluorocarbon is put in contact with the catalyst in the presence of steam to decompose it hydrolytically, could not apply to decomposing processes of other industrial wastes except chlorofluorocarbon, for example organic compounds which have a benzene nucleus, and it could not expect sufficient effects in decomposing efficiency according to the type of chlorofluorocarbon, and furthermore has little durability with the catalyst used for this. It is thus clear to have a problem, that it is not applicable for decomposing mixtures of chlorofluorocarbon and oily substances.
An objective of the present invention, is to provide a system for decomposing environmental contaminants such as chlorofluorocarbon gas, plastics such as polyethylene, woods, organic compounds, which may have benzene nucleus, and other industrial wastes of persistent substances. This system is able to decompose these contaminants under atmospheric pressure or without requiring them to be put under high pressure.
A further objective of the present invention, is to provide a process and a system for decomposing persistent substances, which allows suitably to select substances for constructing it, and to increase decomposition efficiency, or to decompose more easily the mixture of solid components and liquid persistent substances.
To attain these objectives, a process, according to the present invention, characterized by heating a mixture of decomposed substances to be disposed of and a solvent to a predetermined heating temperature, to produce a superheated vapor, and maintaining this superheated vapor for a predetermined reacting time, within a reactor, before passing through this reactor, inside of said reactor being heated at a predetermined temperature under the atmospheric pressure.
Also, the process, according to the present invention, is characterized by heating a mixture of said substances and a solvent to produce a vapor, which is further heating mixture of these substances and a solvent to produce a vapor, which is a further heated up to a predetermined temperature to produce the superheated vapor, and maintaining said superheated vapor for a predetermined reacting time within a reactor before passing through said reactor, inside of said reactor being heated at a predetermined temperature, under the atmospheric pressure.
Further, the process according to the present invention, is characterized by heating a solvent to produce a vapor, which is further heated up to a predetermined temperature to produce a superheated solvent vapor, which will be continuously supplied into a reactor, heated at a predetermined temperature under the atmospheric pressure, supplying said substances into the inside of said reactor, said inside having an atmosphere of said superheated solvent vapor, and maintaining for a predetermined reacting time before passing through said reactor.
Further, the process according to the present invention, is characterized by the fact that the substances to be decomposed, which includes solid matter, are arranged to be maintained for the predetermined reaction time within the reactor before passing through said reactor for discomposing said substances and solid components remaining in the reactor are dropped into a discharging pipe to store in the waste tank.
Still further, the process according to the present invention, is characterized by the fact that the substances to be decomposed, which includes solid matter, are stirred and heated for a predetermined reaction time within said reactor.
Still further, the process, according to the present invention, is characterized by supplying said superheated vapor decomposed with a new solvent into said second reactor.
Still further, the process, according to the present invention, is characterized by cooling said superheated steam, which completes the decomposing process, to liquefy and discharge.
Still further, the process, according to the present invention, is characterized by the fact that the solvent is one or more than one selected from water, methanol, caustic soda, and hydrogen peroxide.
Still further, the process, according to the present invention, is characterized by the fact that the temperature of the superheated vapor is 500xc2x0 C.-750xc2x0 C. when the substances to be decomposed is chlorofluorocarbon.
A further objective of the present invention is to provide a decomposition system for persistent substances, which may comprise a superheated vapor generator means for superheating a mixture of substances to be decomposed and a solvent, to a predetermined temperature to produce a superheated vapor, and an atmospheric pressure reactor means for maintaining said superheated mixture inside thereof to decompose for a predetermined reaction time, inside of said atmospheric pressure reactor means being maintained at a predetermined temperature under atmospheric pressure.
Further, the decomposition system may comprise a vapor generator means for heating a mixture of substances to be decomposed and a solvent to generate a superheated vapor for heating said vapor further to a predetermined temperature to provide a superheated vapor, and an atmospheric pressure reactor means, inside of which is maintained at a predetermined temperature under atmospheric pressure, for maintaining said superheated vapor within thereof for a predetermined reaction time to decompose.
Further, the decomposition system may comprise a vapor generator means for heating a solvent (to generate a solvent vapor), a superheated vapor generator for heating said solvent vapor further to a predetermined temperature to provide superheated solvent vapor, and an atmospheric pressure reactor means for receiving and maintaining said superheated solvent vapor and said substances to be decomposed inside thereof to decompose for a predetermined reaction time, inside of said atmospheric pressure reactor being maintained at a predetermined temperature.
Further, the decomposition system may comprise means which have a transporting means for transporting said substances to be decomposed after said substances elapsed for a predetermined time, said substances including solid components, a discharging pipe for discharging solid components from the reactor, by dropping therefrom, said solid component remained inside the reactor, and a waste tank for storing said dropped solid components inside thereof.
According to the decomposing process of the present invention, organic compounds, which include chlorofluorocarbon gas and benzene nucleus and other persistent substances including environment contaminants, are converted to vapor as well as solvents, which are further heated up from superheated vapor under atmospheric pressure with only its temperature raised, or further it supplied into a superheated solvent vapor atmosphere for maintaining a predetermined reaction time in passing through the reactor thus to become decomposed substances. The superheated vapor which results from the decomposing process is then cooled to liquefy and to discharge. In case of persistent substances including solid components, it is decomposed during passing through the inside of the reactor by a transporting device and remaining solid components are discharged from the reactor. Decomposition may be promoted within the reactor by performing a stiffing process on the substances to be decomposed.